Rand Aldo Leopold was born in Burlington, Iowa on January 11, 1887. His father, Carl Lepold, was a businessman and the nephew of his wife Clara's father, Charles Starker. Rand Aldo was named for two of Carl's business partners—C. W. Rand and Aldo Sommers—although the "Rand" was eventually dropped. The Leopold family included younger siblings Mary Luize, Carl Starker and Frederic. Leopold's first language was German, although he mastered English at an early age.

Aldo Leopold's early life was highlighted by the outdoors; Carl would take his children on excursions into the woods, and taught his oldest son woodscraft and hunting. Aldo showed an aptitude for observation, spending hours counting and cataloging birds near his home. Mary would later say of her older brother, "He was very much an outdoorsman, even in his extreme youth. He was always out climbing around the bluffs, or going down to the river, or going across the river into the woods." He attended Prospect Hill Elementary, where he ranked at the top of his class, and then the overcrowded Burlington High School. Every August, the family vacationed at the forested Les Cheneaux Islands, which the children took to exploring.

In 1900, Gifford Pinchot, who oversaw the newly implemented Division of Forestry in the Department of Agriculture, donated money to Yale University to begin one of the nation's first forestry schools. Hearing of this development, the teenage Leopold decided on forestry as a vocation. In order to be accepted to Yale, his parents agreed to let him attend The Lawrenceville School, a preparatory college in New Jersey. The Burlington High School principal wrote in a reference letter to the headmaster at Lawrenceville that Leopold was "as earnest a boy as we have in school... painstaking in his work.... Moral character above reproach." He arrived at his new school in January 1904, shortly before he turned seventeen. He was considered an attentive student, although he was again drawn to the outdoors; Lawrenceville was suitably rural, and Leopold spent much time mapping the area and studying its wildlife.

Leopold studied at The Lawrenceville School for a year, during which time he was accepted to Yale. Because the Yale Forest School only granted graduate degrees, he first enrolled in Sheffield Scientific School's preparatory forestry courses for his undergraduate studies. While Leopold was able to explore the woods and fields of Lawrenceville daily, sometimes to the detriment of his studying, in Yale he had little opportunity to do so; his studies and social life engagements made his outdoor trips few and far between.

In 1909, Leopold was assigned to the Forest Service's District 3 in the Arizona and New Mexico territories. He was first a forest assistant at the Apache National Forest in the Arizona Territory. In 1911, he was transferred to the Carson National Forest in northern New Mexico. Leopold's career, which kept him in New Mexico until 1924, included developing the first comprehensive management plan for the Grand Canyon, writing the Forest Service's first game and fish handbook, and proposing Gila Wilderness Area, the first national wilderness area in the Forest Service system.

In 1933 he was appointed Professor of Game Management in the Agricultural Economics Department at the University of Wisconsin—Madison, the first such professorship of wildlife management.

He purchased eighty acres in the sand country of central Wisconsin. The once-forested region had been logged, swept by repeated fires, overgrazed by dairy cows, and left barren. There he put his theories to work in the field and eventually wrote his best-selling A Sand County Almanac (1949), finished just prior to his death. Ironically, Leopold, a heavy smoker, died of a heart attack while battling a wild fire on a neighbor's property.

Leopold lived in a modest two-story home close to the campus with his wife and children. His children followed in his footsteps in a variety of ways: Aldo Starker (1913–1983) was a wildlife biologist and professor at UC Berkeley; Luna B. (1915–2006) became a hydrologist and geology professor at UC Berkeley; Nina Leopold Bradley (b. 1917) is a researcher and naturalist; Aldo Carl (1919–2009) was a plant physiologist who also taught at the university until his death; and daughter Estella (b. 1927) is professor emeritus at the University of Washington and a noted botanist and conservationist. Today, Leopold's home is an official landmark of the city of Madison.

Early on Leopold was assigned to hunt and kill bears, wolves, and mountain lions in New Mexico. Local ranchers hated these predators because of livestock losses. However, Leopold came to respect the animals. He developed an ecological ethic that replaced the earlier wilderness ethic that stressed the need for human dominance. Rethinking the importance of predators in the balance of nature resulted in the return of bears and mountain lions to New Mexico wilderness areas.

By the early 1920s, Leopold had concluded that a particular kind of preservation should be embraced in the national forests of the American West. He was prompted to this by the rampant building of roads to accommodate the "proliferation of the automobile" and the related increasingly heavy recreational demands placed on public lands. He was the first to employ the term wilderness to describe such preservation. Over the next two decades he added ethical and scientific rationales to his defense of the wilderness concept. In one essay, he rhetorically asked "Of what avail are forty freedoms without a blank spot on the map?" Leopold saw a progress of ethical sensitivity from interpersonal relationships to relationships to society as a whole to relationships with the land, leading to a steady diminution of actions based on expediency, conquest, and self-interest. Leopold thus rejected the utilitarianism of conservationists like Gifford Pinchot and Theodore Roosevelt.

By the 1930s Leopold was the nation's foremost expert on wildlife management. He advocated the scientific management of wildlife habitats by both public and private landholders rather than a reliance on game refuges, hunting laws, and other methods intended to protect specific species of desired game. Leopold viewed wildlife management as a technique for restoring and maintaining diversity in the environment rather than primarily as a means of producing a shootable surplus.

The concept of "wilderness" also took on a new meaning; he no longer saw it as a hunting or recreational ground but as an arena for a healthy biotic community, including wolves and mountain lions. in 1935 he helped found the Wilderness Society, dedicated to expanding and protecting the nation's wilderness areas. He regarded the society as "one of the focal points of a new attitude—an intelligent humility toward man's place in nature."

His nature writing is notable for its simple directness. His portrayals of various natural environments through which he had moved, or had known for many years, displayed impressive intimacy with what exists and happens in nature. Leopold offered frank criticism of the harm he believed was frequently done to natural systems (such as land) out of a sense of a culture or society's sovereign ownership over the land base — eclipsing any sense of a community of life to which humans belong. He felt the security and prosperity resulting from "mechanization" now gives people the time to reflect on the preciousness of nature and to learn more about what happens there. However, he also writes "Theoretically, the mechanization of farming ought to cut the farmer's chains, but whether it really does is debatable."

A Sand County Almanac

The book was published in 1949, shortly after Leopold's death. One of the well-known quotes from the book which clarifies his land ethic is

A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise. (p.262)

The concept of a trophic cascade is put forth in the chapter "Thinking Like a Mountain", wherein Leopold realizes that killing a predator wolf carries serious implications for the rest of the ecosystem.

Land Ethic

In "The Land Ethic", a chapter of A Sand County Almanac, Leopold delves into conservation in "The Ecological Conscience" section. He wrote: "Conservation is a state of harmony between men and land." He noted that conservation guidelines at the time boiled down to: "obey the law, vote right, join some organizations and practice what conservation is profitable on your own land; the government will do the rest." (p. 243-244)

Leopold explained:

"The land ethic simply enlarges the boundaries of the community to include soils, waters, plants, and animals, or collectively: the land."

"This sounds simple: do we not already sing our love for and obligation to the land of the free and the home of the brave? Yes, but just what and whom do we love? Certainly not the soil, which we are sending helter-skelter down river. Certainly not the waters, which we assume have no function except to turn turbines, float barges, and carry off sewage. Certainly not the plants, of which we exterminate whole communities without batting an eye. Certainly not the animals, of which we have already extirpated many of the largest and most beautiful species. A land ethic of course cannot prevent the alteration, management, and use of these ‘resources,’ but it does affirm their right to continued existence, and, at least in spots, their continued existence in a natural state. In short, a land ethic changes the role of Homo sapiens from conqueror of the land-community to plain member and citizen of it. It implies respect for his fellow-members, and also respect for the community as such."